settings: make slave screen optional and unset by default

doc/config

@@ -407,9 +407,10 @@
 #
 ##
 ## Note: You can define startup slave screen
-## by choosing screen from the list above.
+## by choosing screen from the list above or
+## an empty value for no slave screen.
 ##
-#startup_slave_screen = playlist
+#startup_slave_screen = ""
 #
 ##
 ## Default width of locked screen (in %).

doc/ncmpcpp.1

@@ -272,7 +272,7 @@ If set to "previous", key_screen_switcher will switch between current and last u
 Screen that has to be displayed at start (playlist by default).
 .TP 
 .B startup_slave_screen = SCREEN_NAME
-Slave screen that has to be displayed at start (playlist by default).
+Slave screen that has to be displayed at start (nothing by default).
 .TP 
 .B locked_screen_width_part = 20-80
 If you want to lock a screen, ncmpcpp asks for % of locked screen's width to be reserved before that and provides a default value, which is the one you can set here.

src/ncmpcpp.cpp

@@ -135,10 +135,14 @@ int main(int argc, char **argv)
 	if (Config.startup_screen_type != myScreen->type())
 		toScreen(Config.startup_screen_type)->switchTo();
 
-	// lock current screen and go to the slave one
-	if (Config.startup_slave_screen_type != myScreen->type())
-		if (myScreen->lock())
-			toScreen(Config.startup_slave_screen_type)->switchTo();
+	// lock current screen and go to the slave one if applicable
+	if (Config.startup_slave_screen_type)
+	{
+		auto slave_screen = *Config.startup_slave_screen_type;
+		bool screen_locked = myScreen->lock();
+		if (screen_locked && slave_screen != myScreen->type())
+			toScreen(slave_screen)->switchTo();
+	}
 	
 	// local variables
 	bool key_pressed = false;

src/settings.cpp

@@ -518,10 +518,13 @@ bool Configuration::read(const std::string &config_path)
 	}, defaults_to(startup_screen_type, ScreenType::Playlist)
 	));
 	p.add("startup_slave_screen", option_parser::worker([this](std::string v) {
-		startup_slave_screen_type = stringtoStartupScreenType(v);
-		if (startup_slave_screen_type == ScreenType::Unknown)
-			throw std::runtime_error("unknown slave screen: " + v);
-	}, defaults_to(startup_slave_screen_type, ScreenType::Playlist)
+		if (!v.empty())
+		{
+			startup_slave_screen_type = stringtoStartupScreenType(v);
+			if (startup_slave_screen_type == ScreenType::Unknown)
+				throw std::runtime_error("unknown slave screen: " + v);
+		}
+	}, defaults_to(startup_slave_screen_type, boost::none)
 	));
 	p.add("locked_screen_width_part", assign_default<double>(
 		locked_screen_width_part, 50.0, [](double v) {

src/settings.h

@@ -22,6 +22,7 @@
 #define NCMPCPP_SETTINGS_H
 
 #include <boost/date_time/posix_time/posix_time_types.hpp>
+#include <boost/optional.hpp>
 #include <boost/regex.hpp>
 #include <cassert>
 #include <vector>
@@ -187,7 +188,7 @@ struct Configuration
 	size_t now_playing_suffix_length;
 
 	ScreenType startup_screen_type;
-	ScreenType startup_slave_screen_type;
+	boost::optional<ScreenType> startup_slave_screen_type;
 	std::list<ScreenType> screen_sequence;
 
 	SortMode browser_sort_mode;

src/status.cpp

@@ -140,8 +140,7 @@ void initialize_status()
 #	endif // ENABLE_OUTPUTS
 #	ifdef ENABLE_VISUALIZER
 	myVisualizer->ResetFD();
-	if (myScreen == myVisualizer)
-		myVisualizer->SetFD();
+	myVisualizer->SetFD();
 	myVisualizer->FindOutputID();
 #	endif // ENABLE_VISUALIZER